The human/mouse homology map provides an excellent tool to identify candidate genes involved in human disease. Studies have been initiated using several newly identified loci in man that are candidates for involvement in facial clefting. In collaboration with Dr. Erikson, we have used markers for homologous positions in the mouse to search for QTLs affecting facial clefting. The search identified a region of mouse chromosome 3 homologous to human 1q21 as increasing liability to sporadic CL(P) when the A/J strain allele is present. This effect might be expected since the A/J strain has much higher incidence of sporadic CL9P) than does the C57B16J strain, the other progenitor strain of the RI lines.